1. Technical Field
The embodiments herein generally relate to communication systems, and, more particularly, to techniques for analyzing channel characteristics in digital communication systems.
2. Description of the Related Art
Channel Impulse Response (CIR) is an important metric in describing the channel characteristic in digital communication systems. Channel State Information (CSI) is defined as the channel response to an input stimulate of an impulse signal. In an ideal channel condition, the channel impulse response is a single tap impulse, usually referred to as a main tap. For non-ideal channel conditions, which are usually the case in the real world, echoes due to multi-path reflections exist. These multi-path echoes can be either post cursor echoes which exist after the channel main tap, or pre cursor echoes which exist before the channel main tap.
Multi-path echoes, which are usually unknown to the receiver, for example a Digital Video Broadcasting over Handheld (DVB-H) receiver, can cause inter symbol interference (ISI) in digital communication systems which typically degrade the received signal quality. Accordingly, equalization techniques are employed in the receiver design to remove or compensate for the inter symbol interference caused by the multi-path echoes.
The channel equalization is an important and extensively studied topic in the digital communication world. In order to achieve efficient channel equalization, the knowledge of channel impulse response, or at least the magnitude of the channel impulse response, can be very helpful to design efficient equalization techniques. For example, in wireless communications, the sparseness of the wireless channel impulse magnitude response can be explored to develop efficient equalization algorithms to track very long multi-path echoes in Digital Terrestrial Television (DTV) systems. These techniques require the detection of the individual multi-path location and magnitude out of a noisy background in the channel impulse response. A typical channel impulse magnitude response in a noisy wireless channel is shown in FIG. 1. Other applications of the channel impulse magnitude response detection include making use of the structured channel impulse response characteristic such as the concentrated channel response power distribution to decide the scattered pilot locations in DVB-H devices or Integrated Services Digital Broadcasting (ISDB) for Terrestrial Television/Sound Broadcasting (ISDB-T/ISDB-TSB) systems for fast channel equalization, symbol timing recovery, and carrier frequency synchronizations.
Detection of the location and magnitude of multi-path echoes out of a noisy background in a channel impulse response can be beneficial to the design of efficient channel equalization and synchronization algorithms in modem digital (wireless) communication systems. Existing methods to detect the channel impulse response usually only focus on the global peaks of the noisy channel magnitude response. These techniques usually involve the iterative process of searching for the peak power or magnitude in the channel impulse response, removing it, and then searching for the subsequent largest peaks in the CSI. The computations involved in these techniques can be quite intensive especially when the number of multi-path echoes is large, since multiple sweeps of the channel impulse response is required to detect multiple echoes.
Alternatively, a semi sorting technique can be engaged to detect the first of several largest peaks in the channel impulse response according to certain threshold criteria. However, the computational complexity involved in the sorting-like technique is typically expensive and not generally suitable for application specific integrated circuit (ASIC) implementations. Another drawback for the above peak search type of techniques is the large memory requirement, since the entire channel impulse magnitude response generally has to be stored in memory to enable iterative peak search. Accordingly, there remains a need for a new and efficient technique for detecting the channel impulse magnitude response in digital communication systems.